Validation of microarray data by real-time RT-PCR. (A) The six best discriminators were selected, and the relative expression levels measured by real-time RT-PCR were calculated as levels relative to the housekeeping genes GAPDH, G6PD and RPII in seven of the 60 NCI cell lines: HS-578T, MDA-MB-231, MCF7, T-47D (breast), DU-145 (prostate), HL60, CCRF-CEM (leukemia). Breast: Hs-578T (filled circle), MDA-MB 231 (filled square), MCF7 (filled triangle), T-47D (open square); prostate: DU-145 (open circle); leukemia: HL-60 (open triangle); CCRF-CEM (filled diamond). (B) Analysis of 20 genes contained in the discriminating panel in HS-578T, MDA-MB-231, MCF7, T-47D, DU-145 and HL60 cells. Data are reported as log2 ratio.